# Nested getproperty requests
**URL:** https://discourse.julialang.org/t/nested-getproperty-requests/27968
**Category:** Internals & Design
**Created:** [August 25, 2019, 8:18pm UTC](https://discourse.julialang.org/t/nested-getproperty-requests/27968 "2019-08-25T20:18:25Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@ablaom](https://discourse.julialang.org/u/ablaom)
#### Post date: [August 25, 2019, 8:18pm UTC](https://discourse.julialang.org/t/nested-getproperty-requests/27968/1 "2019-08-25T20:18:25Z")
I have a use for accessing and setting _nested_ properties of julia objects. To achieve this, I have the code below in a package. I have been reasonably accused of type piracy and wondered: (i) if others agree this is dangerous to implement, and (ii) whether julia language developers might conceivably view it as an extension to the language:
```julia
"""
getproperty(object, nested_name::Expr)
Call getproperty recursively on `object` to extract the value of some
nested property, as in the following example:
julia> object = (X = (x = 1, y = 2), Y = 3)
julia> getproperty(object, :(X.y))
2
"""
function Base.getproperty(obj, ex::Expr)
subex, field = reduce_nested_field(ex)
return getproperty(getproperty(obj, subex), field)
end
"""
setproperty!(object, nested_name::Expr, value)
Set a nested property of an `object` to `value`, as in the following example:
julia> mutable struct Foo
X
Y
end
julia> mutable struct Bar
x
y
end
julia> object = Foo(Bar(1, 2), 3)
Foo(Bar(1, 2), 3)
julia> setproperty!(object, :(X.y), 42)
42
julia> object
Foo(Bar(1, 42), 3)
"""
function Base.setproperty!(obj, ex::Expr, value)
subex, field = reduce_nested_field(ex)
last_obj = getproperty(obj, subex)
return setproperty!(last_obj, field, value)
end
# applying the following to `:(a.b.c)` returns `(:(a.b), :c)`
function reduce_nested_field(ex)
ex.head == :. || throw(ArgumentError)
tail = ex.args[2]
tail isa QuoteNode || throw(ArgumentError)
field = tail.value
field isa Symbol || throw(ArgmentError)
subex = ex.args[1]
return (subex, field)
end
```
---
### Author:  [@tkf](https://discourse.julialang.org/u/tkf)
#### Post date: [August 25, 2019, 8:39pm UTC](https://discourse.julialang.org/t/nested-getproperty-requests/27968/2 "2019-08-25T20:39:14Z")
I highly recommend looking at [Setfield.jl](https://jw3126.github.io/Setfield.jl/latest/intro/) which is implemented based on very elegant and simple [lens API](https://jw3126.github.io/Setfield.jl/latest/#Setfield.Lens). Its primary focus is on the immutable data structures at this point but it should not be difficult to extend to in-place operations. Discussion on the support for mutable data structure is happening in [https://github.com/jw3126/Setfield.jl/issues/32](https://github.com/jw3126/Setfield.jl/issues/32)
---
### Author:  [@mauro3](https://discourse.julialang.org/u/mauro3)
#### Post date: [August 26, 2019, 6:39am UTC](https://discourse.julialang.org/t/nested-getproperty-requests/27968/3 "2019-08-26T06:39:47Z")
Maybe of interest [JuliaCon 2018 | Interacting with nested data | Andy Ferris - YouTube](https://youtu.be/vWZzmV7mHiw)